Semisynthesis and antifungal activity of novel oxime ester derivatives of carabrone modified at C(4) against Botrytis cinerea.

To continuously improve the potential utility of the natural lead compound of carabrone in agrochemistry, carabrone oxime and 36 novel oxime ester derivatives of carabrone modified at C(4) were synthesized, and evaluated for their antifungal activities against Botrytis cinerea in vitro and in vivo. Of these 36 oxime ester derivatives, some compounds exhibited antifungal activities in vitro or in vivo. It was found that compounds with a pyridinyl residue can either efficiently inhibit spore germination or efficiently inhibit hyphal growth of B. cinerea, and compound 9 exhibited the highest activity in vitro and in vivo with IC50 and EC50 values of 1.17 and 12.9 μg/ml, respectively. Further, the structure-activity relationships are also discussed.